What Is PrEP?

PrEP stands for Pre-Exposure Prophylaxis. It means taking medicine before being exposed to something to prevent yourself from getting a disease or condition. We use several kinds of medicine this way.

One example is taking anti-malaria medication when we travel to areas where we might be bitten by mosquitoes that carry malaria. When the medicine is in a person's body before getting a mosquito bite, that person is much less likely to get malaria when she or he is bitten.

For women, another example is taking birth control pills (contraceptives). When contraceptives are already in a woman's body when she is exposed to semen during sex, her chances of getting pregnant are greatly reduced.

When we talk about PrEP in connection to HIV and women, we are referring to the idea of HIV-negative women taking HIV drugs to reduce their risk of becoming infected with HIV if they are exposed to it. Some people use the term 'topical PrEP' to describe the use of microbicide gels (e.g., vaginal gels containing HIV drugs). However, in this article when we talk about PrEP, we are referring only to 'oral PrEP,' or HIV drugs taken by mouth as prevention.

How Does PrEP Prevent the Spread of HIV?

Here is how PrEP works:

When CD4 cells are infected with HIV, they become little factories that make thousands of new viruses each day

HIV drugs work by blocking HIV from making copies of itself

If an HIV-negative woman already has HIV drugs in her bloodstream when she is exposed to HIV during unprotected sex, for example, the medicine might be able to keep the HIV from making enough copies of itself to "take hold" and prevent her from becoming infected

Approval for Daily Oral PrEP

Based on the findings of studies mentioned below, in July 2012, the US Food and Drug Administration (FDA) approved the daily use of Truvada (tenofovir plus emtricitabine, or TDF/FTC) as PrEP for sexually active adults at risk of HIV infection. Truvada is a drug often used as part of combination drug treatment for HIV. This is the first time the FDA has approved any drugs for the prevention of HIV.

At the same time, the World Health Organization (WHO) released a recommendation that daily oral PrEP be considered as an additional prevention method for (1) uninfected partners in serodifferent, or serodiscordant couples (one person is living with HIV and the other person is HIV-negative), and (2) transgender women who have sex with men. The WHO approves either Viread (tenofovir) or Truvada for daily oral PrEP.

Currently, PrEP is not available by prescription through the National Health Service in the UK. In Canada, it is available by prescription ‘off label,' as Truvada has not yet been approved for use as PrEP by Health Canada. Gilead, the producer of Truvada, has applied for regulatory approval in several countries; these approvals are pending as of July 2015.

Has PrEP Been Shown to Be Effective?

Several recent clinical trials have shown that taking Truvada as oral PrEP (one pill by mouth daily) can help prevent HIV. These studies were conducted among men who have sex with men (MSM) and transwomen (people who were born male and identify as women) in the US and Latin America, and among heterosexual women and men in several African countries. The effectiveness for Truvada as PrEP varied from 44 percent to 73 percent additional protection against HIV infection in these three studies (known as the iPrex, TDF2, and Partners studies). A study in Bangkok tested oral daily tenofovir (Viread) as PrEP among over 2,400 HIV-negative women and men who inject drugs. It showed that oral daily tenofovir reduced the risk of getting HIV by almost half (50 percent).

Other studies, however, have found these drugs not to be effective in preventing HIV. The FemPrEP study, for example, was stopped early because it did not seem to help in preventing HIV transmission. FemPrEP was testing the effectiveness of oral daily Truvada in Kenyan, Tanzanian, and South African women at high risk for HIV. The VOICE study, which tested oral daily tenofovir, oral daily Truvada (tenofovir plus emtricitabine), and one-percent tenofovir vaginal gel among over 5,000 women in South Africa, Zimbabwe, and Uganda, found all three methods ineffective in preventing HIV transmission.

The Partners Demonstration Project, showed the near elimination of HIV transmission among over 1,000 serodifferent (serodiscordant) heterosexual couples in Kenya and Uganda. The project is testing a combination of PrEP and treatment as prevention. The researchers are offering PrEP as a 'bridge' -- the uninfected partner takes PrEP while the partner living with HIV takes the first six months of antiretroviral treatment. This strategy presumably protects the HIV-negative partner with PrEP during the time it takes for the partner living with HIV to become virally suppressed.

From July 2014 (the study runs through December 2016), only one new infection was noted, representing a 96 percent reduction in infections. Importantly, this reduction in infections applies to all infections, including those from someone other than one's regular sexual partner.

Why Are the Research Findings Unclear?

For any drug or other HIV prevention tool to work, it has to be used; and research tells us that it has to be used correctly and consistently. This is true for condoms and is proving true for PrEP as well. In the studies mentioned above, the key element in PrEP's success was "adherence," which means taking the drug when and how it is prescribed.

In the FemPreEP and VOICE studies, there were low levels of adherence; fewer than one in three women took the drug regularly. Additionally, many women in the FemPrEP study did not consider themselves at risk for HIV. The other studies that showed a benefit had much higher rates of adherence. In all studies, people who took Truvada or tenofovir daily as prescribed were significantly less likely to get infected with HIV when exposed during sex or injection drug use. The US Centers for Disease Control and Prevention (CDC) reports that, in people at high risk for HIV who take PrEP consistently, the risk of HIV infection can be reduced by 92 percent.

We do not yet fully understand all of the reasons why people -- especially women -- have low levels of adherence to oral PrEP. This makes it very important to do more research looking at what issues might affect women's interest in or ability to take a drug for HIV prevention.

It is also important for women to know about and take part in the future research that will look at the unanswered questions about Truvada as PrEP. For more information about understanding, finding, and participating in research studies, see The Well Project's article on Clinical Trials.

This article was provided by The Well Project. Visit The Well Project's Web site to learn more about their resources and initiatives for women living with HIV. The Well Project shares its content with TheBody.com to ensure all people have access to the highest quality treatment information available. The Well Project receives no advertising revenue from TheBody.com or the advertisers on this site. No advertiser on this site has any editorial input into The Well Project's content.

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